1. Brief Description of the Invention
Present invention involves testing of components and electronic sub-systems, such as electrical components using cryogenic fluids to rapidly change temperature of the components.
2. Related Art
The use of environmental testing (ET) techniques such as Environmental Stress Screening (ESS), Accelerated Stress Testing (AST), Highly Accelerated Life Testing (HALT) and Highly Accelerated Stress Screening (HASS) is increasing significantly in the electronics manufacturing. These types of tests are frequently performed on various products ranging from semiconductors, packaged integrated circuits (IC), assembled printed circuit boards (PCBs), fiber-optics devices, or final assembled products (two examples being airplane radar equipment and computer servers). These techniques environmentally strain the manufactured products using stresses that are substantially higher than those experienced in the product life. These tests intend to help precipitate latent defects at minimum costs and in minimum time; detect as many defects as possible at minimum cost and in minimum time; provide the closed loop to failure analysis and corrective actions for all defects found in screening; increase field reliability; and decrease the total cost of production, maintenance, and warranty. In a world where electronics is key to most day-to-day activities, reducing costs and increasing reliability is crucial. For that reason, ET techniques are gaining rapid adoption.
The types of stresses applied to the electronic device vary greatly but most frequently include thermal testing. Thermal testing comprises heating and cooling a device in rapid fashion (up to 100xc2x0 C. xcex94T per minute). The faster the heating or cooling, the better the test is and the faster the products tested can be analyzed and then shipped for repairs or sold on the market. Cooling is typically achieved by using a CFC-based mechanical refrigeration unit or by using cold, cryogenic vaporized liquefied gas that directly contacts the device. The gas used is generally nitrogen as it is relatively safe and it is usually the least expensive commercially inert gas. Other types of gases such as carbon dioxide could be used in certain situations.
The use of vaporized cryogenic liquefied gases is substantial in this art and adds a significant cost to the manufacturing process of the end products. Although generally cost-effective, there is increasing pressure to reduce cryogenic liquid/gas usage and optimize its use. Current systems use mainly a direct injection scheme, where recycling is impossible, or the use of indirect cooling through the use of cooling coils. Typically in both situations the warmed cryogenic gas is vented to the atmosphere.
There is thus a need in the art for better utilization of cryogenic liquefied gas in the ET art, primarily in order to reduce the costs associated with cryogenic liquefied gas usage.
In accordance with the present invention, cryogenic liquefied gas that is used in ET processes is recycled using indirect cooling schemes, in other words, using cooling coils where a cryogenic liquid flows there through. These systems allow recycling of the cryogenic fluid, wherein the term xe2x80x9crecyclingxe2x80x9d includes downstream use of warmed cryogenic fluid after serving its purpose in the ET process.
More specifically, the present invention proposes the use of efficient and improved cooling coils, wherein cryogenic liquefied gas (preferably liquid nitrogen, argon or mixture thereof) enters the coil, where the coils are smartly positioned within an ET chamber, the cryogenic fluid cools the chamber by indirect heat exchange, thus creating a warm cryogenic fluid (at this point either completely gaseous or a mixture of liquid and gas phases). The warmed cryogenic fluid is then sent to a recycling station. The invention comprises thermal cycling (lowering and increasing temperature in cyclic fashion) as well as only cooling, or only heating, but preferred is thermal cooling. Thermal cooling may comprise cooling at a rate ranging from very slow, say 1xc2x0 C. xcex94T per minute, to very rapid, up to about 100xc2x0 C. xcex94T per minute.
As used in the present invention, xe2x80x9crecyclingxe2x80x9d encompasses two primary methods: (a) using a thermosiphon cryogenic vessel and associated equipment, and (b) recompressing the warm cryogenic fluid and/or storing the cryogenic fluid for other plant uses. xe2x80x9cSmartly positioningxe2x80x9d and xe2x80x9csmartly positionedxe2x80x9d as used herein means that the device to be tested and the coils are positioned relative to each other inside the test chamber in a fashion where cooling coils adequately perform their function in raising or lowering the temperature of device. xe2x80x9cAdequately performxe2x80x9d means that the cooling or heating occurs in a precise, controlled manner.
The methods and apparatus of the invention provide significant cost savings to the ET processes. Costs associated with using cryogenic fluids can approach zero when the gas is needed elsewhere in the plant.
A first aspect of the invention is a method of environmental testing of a component (preferably an IC, a PCB, a sub-system, and the like), the method comprising of steps of:
(a) placing a component to be tested into a chamber, the chamber having an internal space filled with a gaseous atmosphere;
(b) indirectly cooling the component by smartly positioning one or more cooling coils near the component to be tested;
(c) feeding the cooling coils with a cryogenic fluid from a source of cryogenic fluid, thus cooling the components and creating a warm cryogenic fluid; and
(d) recycling the warm cryogenic fluid to the source of cryogenic fluid in a thermosiphon fashion using a thermosiphon conduit loop.
Preferred are methods wherein the gaseous atmosphere is non-stagnant (preferably circulated) within the internal space; methods including measuring a temperature of the gaseous atmosphere in the internal space; methods including controlling flow of cryogenic fluid at least partially based on the temperature of the internal space; methods including measuring a temperature of the cryogenic fluid flowing into the coils; and methods including controlling flow of cryogenic fluid at least partially based on temperature of the cryogenic fluid flowing into the coils.
A second aspect of the invention is an apparatus for environmental testing of a component, the apparatus comprising:
(a) a test chamber having an internal space adapted to hold one or more components to be tested.
(b) at least one cooling coil smartly positioned within the test chamber;
(c) a cryogenic fluid feed conduit connecting a source of cryogenic fluid and the coils; and
(d) a cryogenic fluid return conduit connecting the coils to the source of cryogenic fluid, wherein the cryogenic fluid feed conduit and the cryogenic fluid return conduit are connected in a thermosiphon loop.
Preferred are apparatus wherein the test chamber includes means for circulating the gaseous atmosphere in the internal space; apparatus including means for measuring temperature of the internal space of the test chamber; apparatus including means to control the flow of the cryogenic fluid from the cryogenic fluid source.
A third aspect of the invention is a method of environmental testing of a component, the method comprising of steps of:
(a) placing a component to be tested into a chamber, the chamber having an internal space filled with a gaseous atmosphere;
(b) indirectly cooling the component by smartly positioning one or more cooling coils near the component to be tested;
(c) feeding the cooling coils with a cryogenic fluid from a source of cryogenic fluid, thus cooling the components and creating a warm cryogenic fluid; and
(d) flowing the warm cryogenic fluid to a storage device.
Preferred are method including compressing the warm cryogenic fluid to form a compressed cryogenic fluid, and routing the compressed cryogenic fluid to a high pressure storage device; methods including routing at least some of the compressed cryogenic fluid to another use point, the use point selected from the group consisting of other uses on-site, other uses off-site, and storage containers; methods including routing a portion of the warm cryogenic fluid into the internal space; methods including routing a dry gas into the internal space; and methods including vaporizing a portion of the cryogenic fluid in the cryogenic fluid storage container and routing it to other uses.
As used herein the term xe2x80x9cdryxe2x80x9d means a gas containing no more than about 1 percent water, more preferably no more than about 100 parts per million (ppm) water, more preferably no more than 100 parts per billion (ppb) water, most preferably no more than 1 ppb.
A fourth aspect of the invention is an apparatus for environmental testing of a component, the apparatus comprising:
(a) a test chamber having an internal space adapted to hold one or more components to be tested.
(b) at least one cooling coil smartly positioned within the test chamber;
(c) a cryogenic fluid feed conduit connecting a source of cryogenic fluid and the cooling coils; and
(d) a storage device for the warm cryogenic fluid, and a conduit connecting cooling coils to the storage device.
Preferred are apparatus including compression means for compressing the warm cryogenic fluid to form a compressed cryogenic fluid; apparatus comprising a high pressure storage device which takes feed from the compression means; apparatus including a conduit which feeds the compressed cryogenic fluid to other points of use; apparatus including a conduit connecting the source of cryogenic fluid with a heat exchange unit, and a conduit connecting the heat exchange unit with the conduit for supplying alternate uses; apparatus including means for allowing a portion of the warm cryogenic fluid to enter the internal space in the test chamber; apparatus including a temperature measuring means on the test chamber for sensing a temperature of the internal space; apparatus comprising a liquid level sensor on the source of liquid cryogenic fluid; apparatus including control means for controlling the flow out of and flow into the cryogenic storage means; and apparatus including means for delivery of a dry gas to the internal space.
Further appreciation and understanding of the invention will be gained by review of the following description and claims.